Combining different treatment modalities has proven to improve patient outcome compared to applying single treatments. Consequently, mild hyperthermia (HT) and radiotherapy (RT) are combined to radiosensitize tumour cells by inhibiting DNA damage repair mechanisms. In this study, it was investigated if combining both treatment modalities shows an improved therapeutic effect on 3D tumour models made of FaDu cells. To this end, the spheroid size and cell viability were measured over time after treatment. It was also attempted to obtain further qualitative information of the effect on the spheroids using confocal microscopy. During experiments spheroids were formed of FaDu tumour cells, cells of a head-and-neck squamous cell carcinoma, using Matrigel®. These spheroids grew fast within the first 10 days of seeding up to a size of 550-600 𝜇m reliably. These spheroids were then exposed to both single HT and RT as well as combined HT and RT. Both single treatment modalities showed a decrease in cell growth and cell viability with increasing treatment dose. The thermal doses of 30 and 120 CEM43 and radiation doses of 2 and 6 Gy were chosen to be used in the combined treatment experiments. Combined treatment showed an improved effect on the cell growth and cell viability for most treatment groups, both for HT followed by RT and the other way around, with the determining factor seemingly being the thermal dose. The thermal dose of 120 CEM43 combined with 6 Gy of radiation dose showed the highest cell killing potential, with 9±2% of the cell viability remaining when using radiotherapy before hyperthermia and 18±3% when starting with HT before using RT. The most significant difference in effect due to the order in which RT and HT were administered was seen in the group treated with 2 Gy of radiation dose and 120 CEM43 of thermal dose. In this group RT preceding HT resulted in a cell viability of 13±2% on day 7 after treatment, whilst HT preceding RT resulted in a cell viability of 48±8%. Visual inspection of the spheroids showed an increased effect in the form of less growth, as well as flaking around the edges of the spheroids. Obtaining qualitative information on the effect that combined treatment had on spheroids using confocal microscopy was unsuccessful. Both using a live and dead cell staining kit, as well as PI staining proved ineffective in accurately visualizing the dead cells in spheroids.