Dermatitis (skin inflammation) is becoming a serious health problem that lowers the quality of life. Microfluidic devices have been employed as an alternative to conventional in vitro skin models utilized to evaluate irritants, allergens, or drug candidates for dermatitis. However, the following should be achieved: high-throughput analysis by parallelization, simple, easy, and inexpensive device fabrication, and real-time microscopic imaging. In this paper, a photolithography-free skin-on-a-chip for parallel permeation assays is presented. In this study, a consumer laser cutter is employed to form masters for substrates possessing branched microchannel patterns. A porous membrane is sandwiched between the substrates to form 24 crossings of the microchannels on a single device. HaCaT, a human skin keratinocyte cell line, is cultured until confluence on the membrane in the microchannels. Parallel permeation assays are demonstrated using fluorescent-dye-labelled dextran as a tracer and potassium dichromate as an irritant. We think that our technique will expand the use of skin-on-a-chip technology among biologists and pharmacologists, and will open up a new field of biosensing, drug development, and so on.