NOVELTY - A positively-photosensitive siloxane composition comprises 2 or more polysiloxanes (I) which differ by dissolution rate with respect to tetramethylammonium hydroxide aqueous solution, polysiloxane (II) having tetramethylammonium hydroxide aqueous solution-soluble groups other than silanol, diazo naphthoquinone derivative (III), and solvent (IV). The polysiloxane (I) is mixture of polysiloxane (Ia) having dissolution rate of 1000 angstrom/second or less, and polysiloxane (Ib) having dissolution rate of 200 angstrom/second or more.    USE - Positively-photosensitive siloxane composition is used for cured film (claimed), planarizing film for thin-film transistor substrate used for backplane of liquid crystal display element and organic electroluminescent display element, and interlayer insulation film of semiconductor element, solid-state image sensor, antireflection film, reflection preventing board, optical filter, high-intensity light-emitting diode, touchscreen, solar cell and optical waveguide.    ADVANTAGE - The positively-photosensitive siloxane composition has high sensitivity and resolution property. The cured film containing the positively-photosensitive siloxane composition has excellent flatness, electrical insulating property, heat resistance, transparency and remaining-film rate and reduced dielectric constant. The composition provides pattern having reduced defect during image development.    DETAILED DESCRIPTION - A positively-photosensitive siloxane composition comprises 2 or more polysiloxanes (I) which differ by dissolution rate with respect to tetramethylammonium hydroxide aqueous solution, polysiloxane (II) having tetramethylammonium hydroxide aqueous solution-soluble groups other than silanol, diazo naphthoquinone derivative (III), and solvent (IV). The polysiloxane (I) is mixture of polysiloxane (Ia) having dissolution rate of 1000 angstrom/second or less, and polysiloxane (Ib) having dissolution rate of 200 angstrom/second or more with respect to 2.38 wt.% tetramethylammonium hydroxide aqueous solution. The polysiloxane (Ib) in form of film obtained by hydrolytically-condensating silane compound of formula: R1nSi(OR2)4-n (I') in presence of acidic or basic catalyst and prebaking. The polysiloxane (Ia) in form of film obtained by hydrolytically-condensating silane compound (I') in presence of basic catalyst and prebaking is soluble in 5 wt.% tetramethylammonium hydroxide aqueous solution. The mixture of polysiloxanes (Ia) and (Ib) has dissolution rate of 50-1000 angstrom/second with respect to 2.38 wt.% tetramethylammonium hydroxide aqueous solution. The polysiloxane (II) is polysiloxane in form of film having dissolution rate of 50-1000 angstrom/second with respect to 2.38 wt.% tetramethylammonium hydroxide aqueous solution.    R1=6-20C aryl in which H is optionally substituted by fluoro, or 1-20C linear or branched cycloalkyl in which methylene is optionally substituted by O;    R2=1-5C alkyl;and    n=0 or 1.