Electromagnetic field interaction with biological tissues and their applications in cancer treatment research has become of growing interest. This paper describes the possibility of using a slot-line type applicator for microwave hyperthermia treatment in oncology. What we aim to show in this paper is that this type of applicator is particularly suitable for the treatment of superficial cancers with depths 2-3 cm below the body surface. To support this thesis, a 3D electromagnetic field simulator has been used to predict the specific absorbed ratio (SAR), and the consequent temperature distribution in the area under treatment. The results of the simulations are supported by experimental temperature measurements made with the help of an infrared thermo-camera on a homogeneous agar phantom. The possibility to use an array configuration of this applicator in order to treat bigger areas is also analyzed using computer simulation of SAR distribution.