We have designed and constructed a box-type solar cooker with multi-step inner reflectors. The inner reflectors were arranged in a three-step fashion to create different angles with respect to the horizontal. A transient mathematical model is presented for the cooker. It is based on an analytical solution of the energy-balance equations for different components of the cooker. The cooker was tested in the laboratory with a solar simulator under different solar insolation. To validate the present model, numerical calculations have been carried out using the same conditions of indoor tests. The transient performance of the cooker was studied by computer simulation for typical summer (15 July) and winter (15 December) days in Tanta, latitude 30 degrees 47' N, Egypt. Good agreement between experimental and theoretical results is observed. It is evident that the cooker is able to boil 1 kg of water in 24 min when its aperture area equals 1 m(2). The cooker can be used three times a day in summer and twice a day in winter for cooking consecutively with an overall utilization efficiency of about 30%.