Disclosed are a method of making GaAs-based enhancement-type MOS-FETs, and articles (e.g., GaAs-based ICs) that comprise such a MOS-FET. The MOS-FETs are planar devices, without etched recess or epitaxial re-growth, with gate oxide that is primarily Ga2O3, and with low midgap interface state density (e.g., at most 1×1011 cm−2 eV−1 at 20° C.). The method involves ion implantation, implant activation in an As-containing atmosphere, surface reconstruction, and in situ deposition of the gate oxide. In preferred embodiments, no processing step subsequent to gate oxide formation is carried out above 300° C. in air, or above about 700° C. in UHV. The method makes possible fabrication of planar enhancement-type MOS-FETs having excellent characteristics, and also makes possible fabrication of complementary MOS-FETs, as well as ICs comprising MOS-FETs and MES-FETs. The method includes deposition of gate oxide of overall composition GaxAyOz, where Ga substantially is in the 3+ oxidation state, A is one or more electropositive stabilizer element adapted for stabilizing Ga in the 3+ oxidation state, x is greater than or equal to zero, z is selected to satisfy the requirement that both Ga and A are substantially fully oxidized, and y/(x+y) is greater than 0.1.