Technology Sector Performance in S&P 500 Performance

The heatmap groups companies using GICS, the Global Industry Classification Standard, which S&P Dow Jones Indices and MSCI run jointly. GICS splits the index into 11 sectors, and the one labeled Information Technology contains three industry groups: software and services, technology hardware and equipment, and semiconductors and semiconductor equipment.

That definition is narrower than most people's everyday sense of "tech." A company that sells things over the internet or makes money from digital advertising is not necessarily classified here — what matters is what the business sells, not how modern it feels.

Because GICS classifies them elsewhere. Alphabet, Meta, and Netflix sit in Communication Services, on the logic that their revenue comes primarily from advertising and media. Amazon and Tesla sit in Consumer Discretionary, as a retailer and a carmaker respectively.

This is the single most common source of confusion when reading a sector heatmap. If you are trying to gauge how "big tech" performed on a given day, you have to look across at least three blocks, not just the one marked Information Technology.

Information Technology was 38.0% of the index as of June 30, 2026, according to S&P Dow Jones Indices — more than three times the next-largest sector, Financials, at 11.8%. Because the index is weighted by market capitalization, that share moves every day with prices and is not a fixed allocation.

Add Communication Services and the technology-adjacent slice of Consumer Discretionary and the figure climbs well past half the index, which is why the S&P 500's day-to-day direction increasingly tracks a handful of very large companies.

Block size reflects float-adjusted market capitalization — the total value of shares available to public investors. A company worth ten times another gets roughly ten times the area. It has nothing to do with revenue, employee count, or how much the stock moved that day.

This is why the largest semiconductor and software names dominate the technology block visually while dozens of smaller constituents compress into slivers along the edges.

Green means the stock is up on the session, red means it is down, and the intensity of the shade tracks the size of the move. A pale square is a fractional change; a saturated one is a large move. Gray or near-neutral squares are stocks that have barely budged.

Hover any square to see the ticker, current price, and percentage change.

Yes. Click the Technology label on the heatmap to zoom into that block, and the map will redraw using only those constituents, sized against each other rather than against the whole index. Click out to return to the full view.

Viewing tech in context first is often more informative anyway, since it shows you whether a strong day for semiconductors was a sector story or part of a broad market move.

A GICS restructuring in March 2023 dissolved the old data processing and outsourced services category. Payment companies including Visa, Mastercard, PayPal, and Fiserv moved to Financials, while payroll processors such as ADP and Paychex moved to Industrials.

Reclassifications like this happen periodically and can shift several percentage points of index weight between sectors overnight without any company changing what it actually does. It is worth remembering when comparing sector weights across long time spans.

Usually, but not always — and the relationship has tightened considerably. With technology at roughly 38% of the index, a strong day for the sector's largest names is often enough to pull the whole index positive even when a majority of the 500 constituents are lower.

The reverse also happens: broad gains across smaller constituents can be swamped by weakness in two or three mega-caps. Comparing the S&P 500 against its equal-weighted version is the usual way to check which is going on.

The Nasdaq 100 tracks the largest non-financial companies listed on the Nasdaq exchange, so it is defined by listing venue rather than by industry. It is heavily technology-weighted but includes consumer and healthcare names, and it excludes large technology companies listed on the NYSE.

The two indices have converged sharply as technology's weight in the S&P 500 has grown. Their rolling 12-month correlation reached 0.98 in March 2026, an all-time high, meaning they now move in close to lockstep.

The map refreshes through the trading session, so colors and percentages reflect the current day's move. Outside market hours it shows the most recent close.

The index itself rebalances quarterly, in March, June, September, and December, when constituents can be added or removed and share counts updated. Sector weights, however, drift continuously with prices between those dates.