During a survey on insect egg parasitoids in Uşak province (Turkey), parasitized egg clusters of Chlorochroa juniperina (L.) (Hemiptera: Pentatomidae) were collected on Juniperus oxycedrus L. (Cupressaceae). After emergence, the egg parasitoid was identified as Trissolcus semistriatus Nees (Hymenoptera: Scelionidae). This is the first record of this parasitoid reared from the egg masses of C. juniperina. This species has not been previously reported for T. semistriatus as a host species. Mainly eggs of Eurygaster spp. and different pentatomid species were used as hosts in mass culture of the parasitoid. Eggs of this species are acceptable as an alternative host to T. semistriatus during the summer. During 2016 and 2017, 61 egg clusters were collected for the first year and 83 egg clusters were collected for the second year. They have been determined to be parasitized by 31% and 27%, respectively, over the years. Also the rate of emergence and sex ratios were calculated as 98% and 79% in the egg clusters. According to these results, T. semistriatus has an important effect on the populations of C. juniperina under natural conditions in Uşak province of Turkey.