The heat capacity measured through the superconducting transition in ABi2 is shown in Fig. . Bulk nature of the superconductivity is confirmed by large, sharp anomalies at Tc = 4.24 and 4.65 K for RbBi2 and CsBi2, respectively. It is worth noting that under applied field the jump at Tc becomes larger than at zero field in both compounds. Similar effect was observed eg. in KBi2 , ScGa3, LuGa3 44 , YbSb2 45 , ReAl6 , and LiPd2Ge 47 type-I superconductors. The Debye temperature (ΘD ) is calculated from the β specific heat coefficients using the relation: