Indium antimonide magnetoresistors are used for magnetic position sensors in very demanding automotive environments such as crankshaft and camshaft angular position sensors for engine control. Growth of very thin InSb layers is desirable to increase the sheet resistance, which makes it possible to reduce the size of a magnetoresistor. However, the minimum thickness of indium antimonide used in production devices is typically limited to at least 1.5 mu m by crystallographic defects arising from growth on lattice mismatched substrates and by the device requirement of very large electron mobilities. The use of a highly resistive In1-xAlxSb buffer layer was studied to determine its effects on the electron mobility of the InSb active layer. With optimized buffer layers, InSb active layers with 0.55 mu m thickness could be grown with electron mobilities of approximately 40 000 cm(2)V(-1) s(-1) at room temperature and 30 000 cm(2)V(-1)s(-1) at 200 degrees C.