Surfaces which are structured on the micro- and nanoscale to resist wetting are being considered for internal flows due to their drag reducing properties. Here, expressions are developed to characterize the thermal slip in a laminar flow which occurs near the surface for the case when large meniscus curvature is present. The surfaces considered are composed of ridges oriented parallel to the flow. Curvature of the meniscus, which resides between the liquid in the Cassie state and the gas trapped in cavities between the ridges, results from the pressure difference between the liquid and the gas. The meniscus is considered adiabatic. The tips of the ridges have a constant temperature boundary condition. A conformal map is developed to provide an expression for thermal slip for a negative protrusion angle of 90 degrees. Additionally, a conformal map is adapted from the literature to provide a thermal slip expression for a positive protrusion angle of 90 degrees. Both expressions are provided as a function of cavity fraction of the surface. When, a negative protrusion angle exists, heat transfer is enhanced relative to that of a flat meniscus. Conversely, positive protrusion angles reduce heat transfer.