NOVELTY - The semiconductor element comprises a rear-side substrate and a front-side semiconductor layer, and a buffer disposed between the substrate and the semiconductor layer. The buffer is continuously transferred or stepped from a lattice constant of the substrate to a lattice constant of the semiconductor layer, and is present in the growth direction of the semiconductor component having regions (A, B, C...) each having the buffer layer. The regions are formed of different compositions of semiconductors. The buffer increases or decreases the lattice constant in the regions.    USE - The semiconductor element is useful as a multi-junction solar cell, and for power generation in a space satellite or terrestrial photovoltaic concentrator system (all claimed).    ADVANTAGE - The efficient semiconductor element has reduced density of dislocations.    DETAILED DESCRIPTION - The semiconductor element comprises a rear-side substrate and a front-side semiconductor layer, and a buffer layer placed between the substrate and the semiconductor layer. The buffer layer is continuously transferred or stepped from a lattice constant of the substrate to a lattice constant of the semiconductor layer, and is present in the growth direction of the semiconductor component having regions (A, B, C...) each having the buffer layer. The regions are formed of different compositions of semiconductors. The buffer layer increases or decreases the lattice constant in the regions in the growth direction. The crystal lattice in the regions is partially relaxed, and a crystal hardness of the adjacent buffer layers is increased by the different compositions of semiconductors in the growth direction. The semiconductors of the adjacent buffer layers differ in an element of the periodic table consisting of elements of Group III, IV and/or V. The crystal hardness of the buffer layer in the region B is 3-10% higher than the crystal hardness of the buffer layer in the region A. The lattice constant of the front-side semiconductor layer is 1% higher or lower than the lattice constant of the substrate. A gradient of the lattice constant within the regions is 0.5%. The lattice constant of the buffer layers increases or decreases in the growth direction. The crystal lattice in the respective regions is relaxed to 80% of a cubic lattice constant of the semiconductor. The semiconductor component further comprises an excess layer of compound semiconductor disposed between the buffer and the front-side semiconductor layer. The excess layer relaxes 90-100% of the crystal lattice with respect to the front-side semiconductor layer. The buffer has a thickness of 1000-3000 nm. The regions have a thickness of 200-1500 nm.