We report the growth and transport characteristics of stepped InAs/InAs1-xPx quantum wells with AlSb barriers. Electron mobilities and carrier concentrations in these composite stepped quantum wells were studied as a function of growth temperature and phosphorus content. For InAs1-xPx grown at 430 °C substrate temperature (nominal x=0.2), a high 22 500 cm2/V s electron mobility was observed, while 7100 cm2/V s mobility was observed in a single strained InAs1-xPx quantum well layer. Heterostructure field-effect transistors fabricated using the composite quantum wells exhibited increased breakdown voltage and a 14:1 reduction in source-drain dc conduction when compared to a similar InAs-channel device. © 2004 American Institute of Physics.