Successful heating experiments with second, third and fourth harmonic 140 GHz electron Bernstein waves (EBWs) were performed at an extremely high density of above 3 × 1020 m−3 at Wendelstein7-AS (W7-AS). The EBWs were generated by OXB-mode conversion. At medium densities of 1 × 1020 m−3, efficient current drive with first harmonic 70 GHz EBWs could be demonstrated in an overdense plasma for the first time.