Steady flowfields resulting from slot injection at the surface of a flat plate in a freestream with a Mach number of 3.75 and unit Reynolds number of 1.65×107m-1 are simulated, using the compressible mass-averaged Navier Stokes equations and five typical turbulence models. The flowfields with various total pressure ratios of injection to freestream are computed, and comparisons are made with experimental data in terms of the surface total pressure distribution, the length of the upstream separation region, and the height of the Mach surface (i.e. penetration height). Two characteristics of model performances are clarified. Though the upstream separation length and the penetration height are differently predicted by each turbulence model, the correlations between them are nearly same. A Reynolds stress model can reproduce the upstream separation region more reasonably than a k-ε model does, especially for high injection pressure cases.