LiF:Mg,Cu,P,Si (MCPS), a new tissue equivalent phosphor, was synthesized by solid state method. Powder x-ray diffraction and scanning electron microscope were employed to determine the structural features. The dosimetric characteristics, electron spin resonance (ESR) and defect centers of this newly prepared phosphor were investigated. The MCPS phosphor is highly sensitive when compared with LiF:Mg,Ti and LiF:Mg,Cu,P (MCP), with the TL sensitivity being 35 times and 1.3 times higher respectively. The dosimetric peak occurs at 220 °C with a well defined glow curve structure similar to MCP. MCPS phosphor shows a linear dose response till 10 Gy. The minimum detectable dose has been found to be 8 μGy. The thermal stability of the phosphor could be enhanced by 20 °C from 240 °C to 260 °C when compared to MCP. Defect centers formed in the phosphor by gamma irradiation have been studied by ESR to identify the centers associated with the TL process in this phosphor. Thermal annealing experiments reveal the presence of several defect centers. Center I which shows an isotropic g factor of 2.0233 has been found to relate with the TL peaks at 160 °C, 220 °C and 265 °C. Centers II and III are characterized by isotropic g values of 2.0096 and 2.0019 respectively and are attributed to F centers.