The concept of a gas proportional scintillation counter/microstrip gas chamber (GPSC/MSGC) hybrid detector has been developed recently by our group. A CsI coated microstrip plate (MSP), placed in direct contact with the gas filling, substitutes in this detector the PMT commonly used as the UV photosensor in GPSCs. This type of detector combines the advantages of both types of detectors, GPSC and MSGC. Additionally, this photosensor is integrated inside the GPSC body, operating directly within the scintillation gas and avoiding the use of a scintillation window that could be expensive and difficult to handle, and that would absorb some of the scintillation. This is a clear advantage in applications where large detection areas and/or high gas-pressures are needed.