Real‐space transfer (RST) in three‐terminal devices is analyzed in detail with a Monte Carlo model including size‐quantization effects. A double heterojunction structure is considered with In0.25Ga0.75As as the narrow band gap material. Schro¨dinger’s and Poisson’s equations are solved self‐consistently in one dimension to compute the subband energies and wave functions which are then used to calculate scattering rates for the two‐dimensional electron gas. Electrons are injected at one end of the channel segment and the probability of RST, time required for RST etc. are calculated. Variation of these quantities with respect to longitudinal and transverse electric fields and electron density is studied. We point out that this approach is more relevant to a three‐terminal device like the real‐space transfer transistor than previous approaches which focus on steady‐state velocity‐field characteristics. We also compare the results with a semiclassical model that ignores size‐quantization and observe that quantization favors RST due to the subband structure of the quantum well.