Abstract: A fast response, upright sprinkler head includes a body having a central orifice through which fire extinguishing fluid is expelled through an outlet end. A yoke, attached to the exterior surface of the sprinkler body, extends beyond the outlet end of the sprinkler body and is connected at its apex to a deflector. A fusible trigger assembly is coupled to the yoke and the outlet end of the sprinkler head. The deflector is formed with a planar member having a skirt depending therefrom and an annular ledge extending horizontally from the skirt. The skirt depends from the planar member in an outward direction at a pre-selected angle from the vertical, and is formed with a plurality of through-holes. The fast response upright sprinkler head is configured to have a K value of at least 13.5, while the fusible trigger assembly has a fusing temperature between approximately 155° F. and 175° F.