Several properties of semiconducting CaO-PbO-Fe 2 O 3 -P 2 O 5 glasses have been measured. These properties include density, IR, DSC, and DC conductivity. The change in the structure for the present glasses shows that with increasing CaO content there is a corresponding decrease in the number of Q 1 phosphate units and an increase in the non-bridging oxygens (NBOs) as more Q 0 phosphate units are formed in the glass. The decrease in the density, d, and glass transition temperature, T g , is due to the lower degree of cross-bonding between the calcium and NBOs in Q 0 phosphate units resulting in a weakening of glass network. The nearly constant DC conductivity and activation energy for glasses containing p12 mol% CaO is attributed to an ion-polaron interaction which is responsible for the low mobility of the calcium ions that shows no detectable contribution to the DC conductivity. With increasing CaO content, up to 24 mol%, the DC conductivity increases which is directly related to an increase in the mobility of the calcium ions. An increase in the number of non-bridging oxygens that appear in the neighborhood of the calcium ions is responsible for an increase in the ionic conductivity.