Picosecond mid-IR USPL induced surface damage on a Gallium Phosphate (GaP) and Calcium Fluoride $(CaF_2)$ is reported. A semiconductor GaP and a dielectric material $CaF_2$, that are transparent over $3sim10{mu}m$, were exposed to one picosecond mid-IR light $(4.7{mu}m)$ to investigate laser-induced surface morphological changes on the target. The initiation of damage along the polishing scratch line of GaP and the random location of damage digs on the $CaF_2$ suggests that the mid-IR picosecond laser-induced damage on targets started from intrinsic surface defects. Multiple pulse irradiations produced periodic corrugated surface structures (ripples) perpendicular to the polarization of light on both GaP and $CaF_2$. In terms of the orientation and the spacing between ripples, observed ripples have common features with previously reported ripples.