Updated from 4:33 p.m. EDT

Wireless chipmaker Silicon Laboratories ( SLAB) swung to a profit and edged past Wall Street estimates on the top and bottom lines for the quarter ended April 3, though jittery investors knocked some value off the shares in after-hours trading Monday.

The shares were recently down $2.73, or 4.9%, to $53.40, compounding a 21-cent loss to $56.13 in regular Monday trading.

After the bell, the company said first-quarter revenue grew 78% from last year's levels to $113.6 million, above the consensus estimate for $107.3 million.

Quarterly net income totaled $19.9 million, up from a loss of $1 million a year ago. Per-share profit amounted to 36 cents based on generally accepted accounting principles. On a pro forma basis, net profit was 38 cents, 4 cents ahead of expectations.

Chief Executive Officer Dan Artusi said in a statement that demand had been strong in the voice-over-Internet protocol market, notebook computers, and cell-phone handsets.

Silicon Labs drew 54% of its sales from the wireless handsets, flat with the prior quarter. The remaining 46% of revenue reflects sales of chips used in everything from cable and satellite set-top boxes to DSL modems, PC modems, and optical networking equipment.

Leading customer Samsung accounted for 19% of sales in the first quarter, even with the prior quarter.

The chipmaker guided for revenue of $120 million to $123 million in the quarter under way, outpacing the Wall Street consensus estimate of $111.4 million, according to Thomson First Call. On a postclose conference call, management forecast adjusted per-share earnings of 38 cents to 39 cents, excluding a noncash charge. Analysts had been gearing for 35 cents.

At C.E. Unterberg, Towbin, analyst Kalpesh Kapadia said Silicon Labs delivered a solid quarter, notwithstanding the after-hours dip in the stock price. He noted investors might be punishing Silicon Labs for the fact that sales to Samsung stayed flat with the prior quarter, though the handset maker actually saw its share of the market increase. "So there might be a market share loss," he said. "But the silver lining is that they grew wireless sales 4% in a seasonally weak quarter, even with Samsung being flat." (Kapadia has a buy rating on the company; his firm has not done banking for Silicon Labs.)

Another possible reason for the after-hours stock slide: investors may be less apt to give credit for the company's first-quarter performance because a one-time gain of $1.8 million on the sale of equipment could have accounted for some of the upside, noted Sandy Harrison of Pacific Growth Equities. Given the relatively lofty expectations for both Silicon Labs and its peers, investors have been quick to pounce on anything remotely out of the ordinary, he explained. (Harrison has only equal weight rating on the shares; his firm has not done investment banking for Silicon Labs.)

Silicon Labs' business is actually more diverse than the company gets credit for, but the stock has lately traded mostly on wireless sentiment, he explained, and that makes it a potentially volatile play, for now, he said. "If wireless players sneeze, they're going to get pneumonia," he said.