The pertubed angular correlation (PAC) technique was applied to investigate ternary semiconductors of the type AIBIIICV2. The investigations were carried out with 77Br in AgGaSe2, CuInSe2, CdGeAs2 and CdSnAs2 in order to measure the electic field gradient (efg) at the C-sites. The probe atoms were implanted into AgGaSe2 and CuInSe2. In the case of CdGeAs2 and CdSnAs2 the isotop 77Br was produced via the nuclear reaction 75As(α,2n)77Br. The experimental show that the efg at the C-sites is very large and axially asymmetric (η > 0). Calculations of the efg were carried out by a modified de Wette procedure which show a good agreement with the observed results.