Efficient generation, maintaining, manipulation and detection of electron spin polarization and coherence at room-temperature (RT) in semiconductors is a prerequisite for the success of future semiconductor spintronics and quantum information technologies. [1][2][3][4][5] Potential spintronic devices are expected to be based on fundamental building blocks such as spin filters (or spin injectors or spin aligners), spin amplifiers and spin detectors. During the past decade spin filters and spin detectors have been a main focal point of intense research efforts in the field of semiconductor spintronics that have led to many innovative approaches and encouraging developments. [1][2][3][4][5] In sharp contrast, experimental developments in spin amplifiers have so far been extremely limited. This is despite of the facts that many theoretical proposals for a wide variety of model spin amplifiers have been suggested during the past decade, ranging from spin amplifiers using spin injection pillar [6,7] or a dual-drain nonlocal lateral spin valve [8] or non-magnetic semiconductors, [9] unipolar spin transistors, [10] Submitted to 2 magnetic dipolar transistors, [11,12] spin gain transistors, [13] and optically controlled spin transistors. [14] As most of the proposed models require the involvement of a spin-functional diluted magnetic semiconductors (DMS), a lack of true DMS that can provide spin-polarized carriers at RT has so far prevented experimental realization of these proposed spin amplifiers.To our knowledge, the highest temperature at which a spin amplifier has so far been experimentally demonstrated to function is 150 K using a dual-drain nonlocal lateral spin valve based on an ferromagnetic metal-semiconductor hybrid structure. [8] Here we propose and demonstrate a new concept of a defect-enabled spin amplifier based on a non-magnetic semiconductor (Figure 1a). We shall show that a large spin gain (up to 2700 %) can be obtained at RT by employing Ga(In)NAs. This spin amplification functionality is facilitated by the spin-dependent recombination processes via defects, [15][16][17] which was also recently explored for spin filtering. [15,18] Spin amplification in the proposed spin amplifier is self-triggered by incoming conduction electrons with a finite spin polarization regardless of how weak and which direction the spin polarization is. Therefore, the sign of the spin polarization of the outgoing electrons from such a spin amplifier exactly follows that of the incoming electrons. Such spin amplification is generally efficient because even very weak spin polarization of incoming conduction electrons can dynamically polarize the spins of the defect electrons to a much greater degree, thanks to a much longer spin lifetime of the defect electrons commonly known in semiconductors. The spin-polarized defects can then in turn selectively capture and deplete conduction electrons with an opposite spin orientation (i.e. minority spin) governed by the Pauli exclusion principle, leading to greatly enhanced spin polarizat...