Transparent electronic devices have interesting applications in a wide range of fields, such as wearables, intelligent windows, new concepts of smartphones and sensors. In this work we present fully transparent AlN-based thin film bulk acoustic wave solidly mounted resonators. We have used indium-tin oxide as the transparent material for the electrodes and a transparent acoustic reflector consisting of alternating layers of SiO2 and Ta2O5 or WO3, to ensure an adequate acoustic confinement while keeping a high transparency. The fabricated devices display an electromechanical coupling coefficient up to 4% and a quality factor Q of 100. The measured transmittance in the visible spectrum (450 – 750 nm) is 75%.