Photoacoustic tomographic breast imaging systems progressively move into the clinics for in-vivo studies. Next to tumor detection, studies also focus on extracting information about the tumor by performing multi-wavelength photoacoustics for quantitative oxygen saturation estimations. Until now, it has been difficult to compare the results from different systems due to the wide variability in system characteristics and image reconstruction algorithms. In order to do inter-system comparisons in photoacoustic breast imaging, and to validate oxygen saturation estimations, a standardized but realistic measurement object is required. In this study, we present the first 3D semi-anthropomorphic photoacoustic breast phantom and demonstrate its features both in ultrasound imaging as in photoacoustic tomography.