The invention provides an addition-curable silicone composition which provides a cured product having good performance at a low temperature and excellent resistance to a temperature change, and to provide a semiconductor device having a high reliability, whose semiconductor element is encapsulated with the cured product. The invention provides an addition-curable silicone composition comprising (A) a branched organopolysiloxane having at least two alkenyl groups and represented by the formula (1) with a short branch consisting of 1 to 4 siloxane units, (B) an organohydrogenpolysiloxane having at least two hydrosilyl groups, in an amount such that a ratio of the number of the hydrosilyl groups in component (B) to the number of the alkenyl groups in component (A) is 0.4 to 4, and (C) a hydrosilylation catalyst in a catalytic amount. The invention also provides a semiconductor device provided with a cured product obtained by curing the condensation-curable silicone composition.