Reading the Semi Cycle: Book-to-Bill, Lead Times, and Channel Inventory

Semiconductors are cyclical, and the cycle is the trade. Get the phase right and you can be wrong about a lot of other things; get it wrong and the best company in the world will still hurt you. The good news: the industry leaves fingerprints. Three of the most reliable are book-to-bill ratios, lead times, and channel inventory. Used together — never alone — they tell you where you are.

This is a framework piece, not a call. The point is to give you a checklist you can re-run every quarter on your own holdings, whether that's NVIDIA, Texas Instruments, Microchip, or an equipment name like ASML.

What the semi cycle actually is

The semi cycle is fundamentally an inventory cycle layered on top of an end-demand cycle. End demand for chips grows in a long secular line — more compute, more sensors, more connectivity. But the supply chain that fills that demand whips around violently, because:

Lead times for advanced nodes can run 6-12 months. Customers order ahead.
When supply is tight, customers double-order to protect themselves.
When supply loosens, those phantom orders cancel — sometimes all at once.
Distributors sit in the middle, building or burning inventory based on what they think OEMs will need.

The result is a recurring four-phase cycle: shortage, peak, digestion, trough. Each phase has a signature in the three indicators below.

Book-to-bill: a coincident, not leading, indicator

Book-to-bill is the ratio of orders booked to orders shipped (billed) in a period. Above 1.0 means orders are coming in faster than they're being filled — backlog is building. Below 1.0 means the backlog is shrinking.

The SEMI organization publishes a monthly book-to-bill for North American equipment makers. Individual companies — TI, ADI, Microchip, ON Semi — often disclose directional commentary on their calls even if they don't print a clean number.

What to remember:

Above 1.0 is not automatically bullish. Late in a shortage, B2B prints well above 1.0 because customers are double-ordering. That's the most dangerous moment to chase the stock.
Below 1.0 is not automatically bearish. Early in a recovery, B2B can still be below 1.0 while lead times are stabilizing and inventories are clearing. That's often the best entry.
Trend matters more than level. A B2B falling from 1.3 to 1.1 is a more important signal than a B2B sitting at 1.05.

Treat book-to-bill as coincident-to-slightly-lagging. It confirms what's happening; it rarely tells you what's next.

Lead times: the cleanest tell

Lead time is how long between when a customer places an order and when the chip ships. For commodity analog and microcontrollers, normal lead times tend to run in the 8-14 week range. In tight market periods, lead times for some analog and microcontroller parts have extended significantly. When supply normalizes, they collapse back — and the stocks often know it before the earnings do.

Lead times are the cleanest signal because they're hard to fake:

Extending lead times = real or perceived shortage. Customers will start double-ordering. Revenue is about to look great. Be careful what you pay.
Stable, normal lead times = balanced market. Boring is good. Pricing holds.
Compressing lead times = excess capacity or weakening demand. Double-orders start canceling. Revenue guides get cut.

The inflection — the quarter lead times start coming in — is usually where the stocks top, well before reported revenue rolls over. The reverse inflection, when lead times stop compressing and stabilize, is where they bottom.

Distributor inventory: the digestion gauge

Roughly a third of broad-based analog and microcontroller volume moves through distributors — Arrow, Avnet, WPG. Their inventory tells you whether the channel is hungry or stuffed.

The metric to know is weeks of inventory (WOI): how many weeks of forward shipments are currently sitting on distributor shelves. Normal ranges typically in the 7-9 week range for broad-based analog. Above 10 means the channel is overstocked and orders to the chipmaker will be cut regardless of end demand. Below 7 means the channel is lean and any uptick in end demand will require restocking — a tailwind to chipmaker revenue beyond the underlying demand pulse.

Two nuances:

Watch the direction more than the level. WOI rising for two quarters in a row is a yellow flag even if it's still in the normal range.
Some chipmakers manage to distributor sell-through, not sell-in. TI is the obvious example — they report based on what distributors ship to end customers, not what they ship to distributors. That removes one layer of distortion but doesn't remove the cycle.

Putting the three signals together

No single indicator is enough. The phases roughly map like this:

Shortage / early peak: B2B well above 1.0, lead times extending, distributor inventory below normal. Stocks usually already up a lot. Risk: paying peak multiples on peak earnings.
Late peak: B2B still above 1.0 but flattening, lead times stop extending, distributor WOI starts creeping up. The setup for a downcycle.
Digestion: B2B below 1.0, lead times compressing fast, distributor WOI elevated. Estimates getting cut. Stocks generally falling.
Trough: B2B still soft but stabilizing, lead times at or below normal, distributor WOI working back to normal. End demand commentary is awful. This is typically the entry point.

The hardest emotional part is that the trough signal looks exactly like bad news. You're buying the quarter where management says visibility is poor, because the inventory math says the next order cycle has to come.

What to watch next

Pull the SEMI book-to-bill release each month and chart the six-month trend, not just the print.
On every analog/MCU earnings call you care about, search the transcript for "lead times" and "channel inventory" — management language shifts before the numbers do.
Track distributor weeks-of-inventory by reading Arrow's and Avnet's quarterly results alongside your chipmaker holdings.
Write down which phase you think the cycle is in before each earnings season and grade yourself afterward. Cycle calls only get better with reps.