The vapoluminescent characteristics of platinum(II) double salt materials in the presence of varying levels of relative humidity (RH) have been investigated. Luminescence spectra for three different platinum(II) double salt materials showed that the intensity and the wavelength maximum depend on the concentration of water vapor surrounding the material. Partial least squares (PLS) analysis of the data demonstrated that two of the double salts responded linearly to changes in RH. A single-channel dip probe sensor was constructed and used to evaluate changes in RH. Different methods for attaching the platinum(II) double salt material to the dip probe were also investigated. Simple adsorption of the material onto the probe produced a sensor with superior performance compared to a Teflon AF support matrix. The PLS analysis of simultaneous three-channel cross-reactive sensor array data from three different platinum(II) double salt materials yielded a much more reproducible RH sensor. In addition, the three-channel cross-reactive array produced a more linear PLS model compared to a single-channel sensor composed of a simulated mixture of the same three platinum(II) double salt materials.