NEW YORK (AP) ¿ Supertex Inc. shares fell Wednesday after the chip maker's fiscal second quarter profit missed Wall Street forecasts as its profit margin shrank. The stock tumbled $3.11, or 10.7 percent, to $25.91 in afternoon trading. Late Tuesday, Supertex reported net earnings of $1.1 million, or 8 cents per share, compared with $4.5 million, or 35 cents per share, in the same quarter a year ago. Sales dropped 32 percent to $15.9 million. Analysts polled by Thomson Reuters expected 10 cents per share on sales of $14.8 million. Supertex said its second-quarter gross margin was 47 percent, six percentage points lower than in the first quarter. It attributed the drop to "the non-linear loading of our wafer fab and backend operations." CEO Henry Pao said he expects the gross margin in the company's third quarter to be similar to the second quarter number, noting that Supertex is planning a normal wafer fabrication facility shutdown for maintenance. In a note to investors, Morgan Keegan analyst Harsh Kumar attributed Supertex's earnings miss primarily to the lower gross margin and said the margin is being hurt because its factories are operating below capacity. He reiterated a "market perform" rating on the stock.