A one-pack type curable silicone gel composition which contains: 100 parts by mass of (A) a branched chain organopolysiloxane having a specific structure from 0.1 part by mass to 50 parts by mass of (B) a diorganopolysiloxane having both molecular chain ends blocked with diorganohydrogensiloxy groups; (C) a platinum-based catalyst; and (D) a phosphite compound represented by formula (3)




(wherein R2 represents a monovalent aliphatic hydrocarbon group having 1 to 10 carbon atoms; and X represents a hydrogen atom or a methyl group)

in such an amount that more than 3 molecules hut not more than 15 molecules of the phosphite compound represented by formula (3) are present per one platinum atom in component (C). This one-pack type curable silicone gel composition is stable in terms of characteristics and physical properties even if exposed to a temperature more than 50° C. for a long period of time.