Supertex ( SUPX) plunged 35% after missing third-quarter financial targets and shaking up its executive suite.The Sunnyvale, Calif., chip company said Richard Siegel quit as executive vice president and as a member of the board to pursue other opportunities. The company named founder and senior vice president of technology Benedict Choy to replace Siegel on the board. Siegel's executive vice president post won't be filled. Supertex also promoted Ahmed Masood to vice president of marketing from director of marketing, and Michael Tsang to vice president of standard products for medical ultrasound, telecom and LED markets from director of standard products for these markets. For the quarter ended Dec. 31, Supertex made $3.7 million, or 26 cents a share, up from $2.3 million, or 17 cents a share a year earlier. Revenue rose to $19.9 million from $14.9 million a year ago. Analysts were looking for a 35-cent profit on sales of $21.7 million. Late Thursday, Supertex fell $15.33 to $27.92.