The present invention relates to a medical device for substantially sized and uniform ablation of animal or human tissue comprising a bipolar generator for generating radio frequency at an electrode, a polarity alternator, an applicator probe having a handle and an elongated member, and a tip at the far end of the distal end suitable for insertion into tissue. The elongated member has a proximal and distal end with an electrode cluster of three or more electrodes located on the distal end of the elongated member. The electrodes are electrically insulated from each other and at least two of the electrodes have dissimilar polarity from each other wherein at least one of the electrodes has a high voltage polarity and at least one of the electrodes has a return polarity. During ablation, the polarity alternator automatically and repeatedly changes the polarity of the electrodes to cycle lesion formation along the length of the electrode cluster and alternate lesion formation repeatedly from one polarity to other polarity to form a spherical or near spherical lesion at the distal tip equal in diameter to the length of the cluster.