The Gediz Graben possesses the second highest geothermal power generation potential in Western Anatolia, Turkey. In this study, the geothermal resource potential of the Gediz Graben has been assessed by following an ideal point methodology. For this purpose, nine criteria layers were introduced into a GIS environment, namely, distance to faults and fault density, distance to cap rock units, hot springs and graben center, Gutenberg-Richter b-value map, night-time surface temperature, NDVI and slope. Each layer was weighted by using the pairwise comparison method. Then, an ideal point methodology, namely, Technique for Order Preference by Similarity to the Ideal Solution (TOPSIS) was used to rank the geothermal favorability of the Gediz Graben from most favorable to least favorable. In order to assess the success of the geothermal favorability map, a comparison of the favorability classes with the known producing well data revealed that 76% of the wells fell within the highest two favorability classes where none of the wells were located in the least two favorable classes.