Aehr Test Systems' products don't test air, but rather silicon. Aehr (pronounced "air") makes gear that tests logic and memory semiconductors to weed out defective devices. Its burn-in systems test chips' reliability under stress by exposing them to high temperatures and voltages. Aehr also makes massively parallel test systems for handling thousands of chips simultaneously, die carriers for testing unpackaged chips, custom-designed fixtures for test equipment, and other memory test products. Top customers include Spansion (about 80% of sales) and Texas Instruments. Aehr gets more than one-third of its business outside the US.