MOS high-k/metal devices with Ge and GaAs semiconductors were used to fabricate PMOS and NMOS devices, respectively. Selective, epitaxially grown (SEG) Ge PMOSFETs exhibit a 2× enhanced IDsat, and greater than 2× improvement in hole mobility compared to Si PMOSFETs. Buried-channel (BC) Ge1-xCx PMOSFETs showed a 2× enhancemsnt in IDsat over Si control PMOSFET and ∼1.5× improvement in effective mobility over universal curve for Si. The corresponding enhancement for surface channel (SC) Ge1-xCx PMOSFETs was 3times; and ∼2.5times;, respectively. The Ion/Ioff ratio for (BC) Ge1-xCx was greater than 5×104. GaAs NMOS capacitors using two different chemical surface treatments NH4OH and (NH4)2S prior to ALD-Al2O3 deposition were examined. Both treatments remove AS2O 3/AS2O6 upon Al2O3 deposition and unpinned the Al2O3/GaAs interface. However (NH4)2S has better frequency dispersion behavior and slightly smaller capacitance equivalent thickness (CET) than NH4OH treatment. Quasi-static CV measurement confirmed formation of a true inversion layer in GaAs.