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We studied the pressure-induced superconductor CeIrSi 3 with the non-centrosymmetric tetragonal structure under high pressure. The electrical resistivity and ac heat capacity were measured in the same run for the same sample. The critical pressure was determined to be P c ¼ 2:25 GPa , where the antiferromagnetic state disappears. The heat capacity C ac shows both antiferromagnetic and superconducting transitions at pressures close to P c . On the other hand, the superconducting region is extended to high pressures of up to about 3.5 GPa, with the maximum transition temperature T sc ¼ 1:6 K around 2.5 -2.7 GPa. At 2.58 GPa, a large heat capacity anomaly was observed at T sc ¼ 1:59 K. The jump of the heat capacity in the form of ÁC ac =C ac ðT sc Þ is 5:7 AE 0:1. This is the largest observed value among previously reported superconductors, indicating the strong-coupling superconductivity. The electronic specific heat coefficient at T sc is, however, approximately unchanged as a function of pressure, even at P c .

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