Single crystals of Gd$_3$ Ga$_3$ Al$_2$ O$_{12}$:Ce,B were grown and coupled to Si-based photosensors, i.e. avalanche photodiode (APD) and silicon photomultipliers (SiPM), to develop a compact yet efficient thermal neutron detector.The performance of a GGAG:Ce,B/CsI:Tl phoswich coupled to SiPM is also studied for the detection and the discrimination of thermal neutrons in the presence of gamma background. The observed characteristic peaks around 35 and 78 keV corresponding to low-energy X-rays and conversion electrons resulting from the thermal neutron capture are found to be well discriminated from the gamma background.