A silicone gel composition for use in sealing or filling of electrical or electronic parts comprising: (A) an organopolysiloxane containing alkenyl groups, having a viscosity of from 10 to 10,000 mPa·s at 25°C as measured by a type-B viscometer according to JIS K 7117-1 and comprising (A-1T) an organopolysiloxane containing alkenyl groups, wherein the organopolysiloxane has a branched structure having at least one siloxane unit represented by RSiO 1.5 , where R represents a monovalent hydrocarbon group, and has from 0.10 to 1.00 mass% of vinyl group moieties (CH 2 =CH-) in a molecule and a viscosity of from 10 to 5,000 mPa·s at 25°C; and (A-2L) a linear organopolysiloxane containing alkenyl groups only at both ends of its molecular chain, having a viscosity of from 50 to 10,000 mPa·s at 25°C where the weight ratio of component (A-1T) / component (A-2L) is 0.85 or less; (B) a linear organopolysiloxane containing hydrogen atoms bonded to silicon atoms at least at both ends of its molecular chain and having a viscosity of from 1 to 10,000 mPa·s at 25°C, in an amount wherein a quantity of the hydrogen atoms bonded to silicon atoms is from 0.2 to 5 moles per 1 mole of alkenyl groups contained in component (A); (C) a catalytic amount of a hydrosilylation reaction catalyst; and (Z) at least one adhesion promoter; which composition is curable to form a silicone gel having 1/4 consistency as stipulated in JIS K 2220 of from 10 to 80, and at 25°C, a shear frequency of 0.1 Hz and strain of 2%, a loss elastic modulus of from 5.0 × 10 2 to 1.0 × 10 4 Pa (5.0 × 10 3 to 1.0 × 10 5 dyne/cm 2 ), a complex elastic modulus of from 5.0 × 10 3 to 1.0 × 10 5 Pa (5.0 × 10 4 to 1.0 × 10 6 dyne/cm 2 ), and a loss tangent of 0.3 or less, such moduli and loss tangent measured by a dynamic viscoelasticity measurement apparatus manufactured by Rheometrics, Inc. (product name: Dynamic Analyzer ARES) at 25°C, shear frequency 0.1 Hz, strain 2%, using a circular plate of silicone gel with a thickness from 5 to 6 mm and a diameter of 25 mm created by heating the silicone gel composition for 1 hour at 80°C. (A) an organopolysiloxane containing alkenyl groups, having a viscosity of from 10 to 10,000 mPa·s at 25°C as measured by a type-B viscometer according to JIS K 7117-1 and comprising (A-1T) an organopolysiloxane containing alkenyl groups, wherein the organopolysiloxane has a branched structure having at least one siloxane unit represented by RSiO 1.5 , where R represents a monovalent hydrocarbon group, and has from 0.10 to 1.00 mass% of vinyl group moieties (CH 2 =CH-) in a molecule and a viscosity of from 10 to 5,000 mPa·s at 25°C; and (A-2L) a linear organopolysiloxane containing alkenyl groups only at both ends of its molecular chain, having a viscosity of from 50 to 10,000 mPa·s at 25°C where the weight ratio of component (A-1T) / component (A-2L) is 0.85 or less; (A-1T) an organopolysiloxane containing alkenyl groups, wherein the organopolysiloxane has a branched structure having at least one siloxane unit represented by RSiO 1.5 , where R represents a monovalent hydrocarbon group, and has from 0.10 to 1.00 mass% of vinyl group moieties (CH 2 =CH-) in a molecule and a viscosity of from 10 to 5,000 mPa·s at 25°C; and (A-2L) a linear organopolysiloxane containing alkenyl groups only at both ends of its molecular chain, having a viscosity of from 50 to 10,000 mPa·s at 25°C where the weight ratio of component (A-1T) / component (A-2L) is 0.85 or less; (B) a linear organopolysiloxane containing hydrogen atoms bonded to silicon atoms at least at both ends of its molecular chain and having a viscosity of from 1 to 10,000 mPa·s at 25°C, in an amount wherein a quantity of the hydrogen atoms bonded to silicon atoms is from 0.2 to 5 moles per 1 mole of alkenyl groups contained in component (A); (C) a catalytic amount of a hydrosilylation reaction catalyst; and (Z) at least one adhesion promoter; <EOS>