Teradyne Inc. shares plummeted more than 10% in after-hours trading Tuesday after the company said demand for testing mobile devices is cratering. Teradyne, which makes equipment for testing semiconductors and other equipment, reported better-than expected first-quarter results, but issued a forecast well below analysts' projections for the second quarter. "Despite the strong first quarter results, the demand outlook for 2018 mobile device test capacity declined sharply in the quarter and our second quarter guidance reflects that revised outlook," Chief Executive Mark Jagiela said in Tuesday's announcement. Teradyne reported first-quarter profit of $87 million, or 43 cents per share, on sales of $487.5 million, up from $456.9 million a year ago. The company claimed adjusted earnings of 45 cents a share, up from 44 cents a share a year ago. Analysts on average expected adjusted earnings of 42 cents a share on sales of $478.4 million, according to FactSet. For the second quarter, however, Teradyne forecast adjusted earnings of 45 cents a share to 52 cents a share on sales of $490 million to $520 million, much less than analysts expected ahead of an expected smartphone refresh cycle. Analysts on average expected adjusted earnings of 93 cents a share on sales of $690 million, similar to the prior year's results. Teradyne stock fell about 11% in late trading after the results were released.