To detect air fluorescence generated from cosmic rays with energies exceeding 1019 eV, which are rare events that produce small light flashes at the detector, a large-area, high sensitivity UV (300-400 nm), single-photon detector is needed. Radiation Monitoring Devices, Inc. (RMD), proposes to design and develop large-area solid-state photomultipliers (SSPMs) based on wide band-gap materials. As the intrinsic carrier concentration is directly related to the band gap of the material, the thermally generated dark current associated with WBG materials will be much lower than silicon for a sufficiently small defect density in the bulk material. The proposed WBG SSPMs will have high gain (105-106), low noise (100 times lower than similar size Si based device), fast response (<5ns), high detection efficiency (>50%) and sensitivity to a single photoelectron at wavelengths between 300 and 400 nm. In phase-I efforts we will explore different design options to improve detection efficiency, response time of the GPD structure. Based on improved GPD structures we will design and fabricate 3mm x 3mm WBG SSPMs. Finally, its basic performance will be evaluated and compared to SSPMs from other vendors and PMTs. The Phase-II effort will develop the large-area multi-element devices and the readout for imaging.