Ga0.47In0.53As JFETs and MESFETs have been fabricated with a lattice-mismatched GaAs layer under the gate. The GaAs could be grown with good electrical and crystallo-graphic quality in spite of the large lattice mismatch by an OM-VPE process. Pn, Np and Schottky diodes were fabricated and applied to n-GaInAs FET channels. Both types of devices exhibited high transconductances of about 100 mS/mm.