Ternary semiconductors AB(5)C(8)(A = Cu/Ag, B = In and C = S, Se or Te) have been investigated. The CuIn(5)S(8)and AgIn(5)S(8)have been synthesize in cubic spinel structure with space group (Fd3m), whereas CuIn5Se8, AgIn5Se8, CuIn(5)Te(8)and AgIn(5)Te(8)have tetragonal structures with space group P-42m. The relaxed crystal geometry, electrical properties such as electronic band structure and optoelectronic properties are predicted by using full potential method in this work. For the determination of relaxed crystal geometry, the gradient approximation (PBE-GGA) is used. All the studied compounds are semiconductors based on their band structures in agreement with the experimental results, and their bulk moduli are in the range 35 to 69 GPa. Wide absorption peaks appeared in the visible to ultraviolet energy region indicating good absorption ability of these compounds. Therefore, these semiconductors are an excellent choice for optical devices, electrochemical and photovoltaic cells. These compounds have remarkable characteristics such as direct as well as indirect band gaps with very slight difference between the two, high absorption coefficient, good photo-stability, easy inter-conversion between n- and p-type semiconductors and in manufacturing of comparatively cheap homo and hetero junction structures.