We present the results of investigations of the growth of two semiconductor materials using supersonic jets. Homoepitaxial growth of GaAs films was accomplished by directing a supersonic jet of the single source precursor (t-Bu)(2)(Ga-As)(t-Bu)(2) seeded in helium at a heated GaAs(100) substrate. Epitaxial GaAs films were produced with substrate temperatures of 400-500 degrees C,while a wafer temperature of 300 degrees C yielded degraded crystallinity in the deposited film. Atomic force microscopy revealed that the GaAs films were relatively smooth,, with a root mean square roughness of 8.1 Angstrom. We have also successfully grown GaN films on sapphire (0001) using supersonic jets of nitrogen atoms and a gallium effusion source. The nitrogen atoms were generated from a mixture of 1% N-2 in He by a radio frequency discharge. A growth rate of 0.65 mu m/h was obtained, independent of substrate temperature over the range 600-750 degrees C. The films were single crystalline wurtzite GaN as determined by x-ray diffraction and in situ reflection high energy electron diffraction (RHEED). The peak width of the (0002) GaN re flection, as measured by high resolution x-ray diffraction, was as low as 38 arcmin, indicating a crystalline quality that is comparable to GaN films deposited by other plasma-assisted molecular beam epitaxy techniques, but inferior compared to films currently grown by metalorganic chemical vapor deposition. In addition, the peak width decreases with increasing growth temperature, indicating that the crystalline quality of the film improves. The RHEED images also indicate that the GaN films have a rough surface morphology.