In order to accomplish spin-based photoelectric information processing, it is necessary to modulate electron spin polarization in III-V semiconductor quantum dots (QDs) using an electric field. However, there is a principal limitation to the spin polarization degree and its control range, as the electron spin polarization is rapidly lost during injection into the QDs at room temperature (RT). Here, electric field control of optical spin polarization in the range of 15-40% is demonstrated at RT using InAs QDs tunnel-coupled with a defect-functional GaNAs quantum well (QW) spin filter. This compares with an electric field control of 1-4% for InAs QDs tunnel-coupled with an InGaAs QW. Transient polarization in the range of 30-60% is also obtained in the ultrafast time domain of less than 100 ps, the degree of polarization depending on the electric field. The enhanced polarization control is achieved by tuning the amplified spin polarization of electrons tunnel-injected from the GaNAs QW into QDs via the electric-field-dependent spin-filtering efficiency of GaNAs. These findings will provide a new way to extensively modulate the electron spin polarization in opto-semiconductors, by electric-field-induced on/off switching of spin amplification.