A fabrication process for n-channel SiGe modulation-doped field-effect transistors has been developed in which the strain in the heterostructure is completely preserved by taking into account an appropriate temperature range for the formation of ohmic contacts to source drain by implantation. It yields a low specific contact resistance of 7.1 x 10(-5) Omega cm(2) to be compared to 5.7 x 10(-2) Omega cm(2) for alloyed Au/Sb contacts. With the same thermal upper limit the application of different gate oxides has been studied. All oxides show negligible gate leakage enabling a superior gate voltage swing compared to devices with a Schottky gate. Application of thermal oxide grown at 650 degrees C yields a superior field-effector transistor performance compared to devices with sputter and plasma-enhanced chemical-vapor deposition deposited oxides due to its lower and negative charge level. Gate recessing of 0.5 mu m Schottky gates yields a transconductance increase up to 310 mS/mm.