Embodiments of High-Power Millimeter-Wave Oscillators are generally described herein. Other embodiments may be described and claimed. In some embodiments, the oscillator includes a polarized partial reflector to at least partially reflect back signals to a reflection array amplifier to help induce oscillation by individual sub-array amplifier elements of the reflection array amplifier. In some other embodiments, the oscillator includes a phase-graded polarization-sensitive reflection plate to at least partially reflect back signals to the reflection array amplifier to help induce an oscillation by the sub-array amplifier elements. In some embodiments, the oscillator includes a reflector and a phase-graded polarized reflection-transmission plate to at least partially pass through signals to the reflector for reflection back to the reflection array amplifier to help induce an oscillation by the sub-array amplifier elements.