The production of stomata, the epidermal pores of plants, is influenced by diverse environmental signals including high temperature. To assess its impact on stomatal formation, researchers need to grow plants in a carefully designed regime under controlled conditions and capture clear, microscopic views of the epidermis. Here, we describe a procedure to study the effect of high temperature on stomatal formation. This method can generate high-quality epidermal images of cotyledons, leaves, and hypocotyl of young Arabidopsis seedlings, which allow the determination of the pattern, density, and index of stomata on these tissues. Besides temperature, the protocol can serve as a general approach to examine stomatal phenotype and the effect of other external signals on stomatal formation.