The bonding quality of silicon wafers used in SOI technology, [1] was estimated by the application of infrared transmission measurements. The investigated wafers were directly welded at high or low temperature by using an intermediary layer. Uniform and extended radiation source was applied. The intensity of the radiation transmitted through the wafer was recorded by the thermovision camera scanning the sample. The proposed way of the experiment, enabled very fast transmission visualization of the entire wafer surface and rough estimation of bonding quality. The more exact analysis of the geometric parameters of the measurement set-up and transmissions of ideal and real semiconductor wafers shown below, enabled in some cases the determination of the sort and size of defect occurring between the bonding wafers.