The influence of in-plane magnetic field on spin polarization in the presence of the oft-neglected k³k3-Dresselhaus spin–orbit coupling was investigated. The k³k3-Dresselhaus term can produce a limited spin polarization. The in-plane magnetic field plays a great role in the tunneling process. It can generate the perfect spin polarization of the electrons and the ideal transmission coefficient for spin up and down simultaneously. In energy scale, complete separation between spin up and down resonance was obtained by a relatively higher in-plane magnetic field while a comparatively lower in-plane magnetic field vanishes the spin separation. On the other hand, the spin relaxation can be suppressed by compensating the oft-neglected k³k3-Dresselhaus spin orbit coupling using a relatively lower in-plane magnetic field.