Two aspirating hot-film probes are developed to make measurements in supersonic air/helium shear layers. The first probe is designed to measure local mean gas composition and is referred to as the mean concentration probe. This probe consists of a constant temperature hot-film sensor operating in a channel with a choked exit. The flow over the hot-fifm is influenced only by total temperature, total pressure, and gas composition. The mean probe is easily calibrated and shows acceptable sensitivity to flow angularity. The second probe is based on an improved design of the mean concentration probe. In addition to measuring mean composition, this second probe also measures turbulence intensities of Reynolds number and thermal conductivity using a multiple overheat method. This probe is referred to as the turbulent probe. Both probes are used in the study of supersonic air/helium mixing layers in the VPI&SU 23 cmx23 cm Supersonic Wind Tunnel. Profiles of mean and turbulent quantities are presented. / Master of Science