The a-MoO3 crystals were grown on Si(1 0 0) substrate from molybdenum oxide vapor at hot zone temperature T¼660 1C by t¼7.2–25.2 ks. Just before the experiment the Si(1 0 0) substrate was subjected to RCA cleaning in diluted HF acid to remove a layer of native oxide [33]. Initially purified molybdenum oxide (99.99%) was used as a source. Crystal growth was produced in horizontal nonflowing tube open-type quartz reactor. A molybdenum oxide charge of1 g in weight was positioned into most hot closed corner of reactor. Molybdenum oxide mass transfer is provided by temperature gradient from closed to open end of the reactor. Siliconsubstrate with 1 cm2 area was positioned by 0.8 cm away the molybdenum oxide charge. As a result of growing, white transparent platelet crystals with dimensions of 1000 200 0.4 mm3 were found on Si substrate and adjacent reactor walls. Micromorphology and chemical composition of the crystals were evaluated with SEM and EPMA by LEO 1430 device.