The present study investigates regional cloud characteristics over the tropical northwestern Pacific using Tropical Rainfall Measuring Mission (TRMM) data sets such as rain rate, radar reflectivity, and passive microwave radiometer polarization corrected temperature (PCT). In particular, the tropical northwestern Pacific is divided into two surface rain maxima regions: the South China Sea (SCS) and the Philippine Sea (PS). The TRMM variables are retrieved by a pair of spaceborne microwave sensors, Precipitation Radar (PR) and TRMM Microwave Imager (TMI). It is revealed that the SCS contains more frequent deeply developed convective systems relative to the PS on the basis of the analysis of the PR and TMI version-6 data during a 4-year period (1998--2001) of summers. This is mainly indicated by two factors: strong PR reflectivity (≥30 dBZ) above the freezing level (~5 km) and TMI ice-scattering signature (PCT at 85.5 GHz ≤ ~190 K, and PCT at 37.0 GHz ≤ ~260 K), which are more frequent over the SCS than over the PS. Comparison of TMI and PR rain rates, a relatively small (large) positive PR--TMI bias is observed for an average of rainy areas over the SCS (PS). This region-dependent PR--TMI bias can arise from the regionally different extents of both (1) the PR's underestimate by attenuation correction and (2) the TMI's overestimate by emission from the melting layer (i.e., SCS > PS in (1) and (2)). These differences are due to the excess of heavy rainfall events, high rain rates, strong convective intensities, and high cloud top heights in the SCS compared with the PS.