NOVELTY - An organosiloxane block copolymer comprising diorganosiloxane units (65-90 mol.%), where the diorganosiloxane units are arranged in linear blocks having an average of 10-400 diorganosiloxane units per linear block; and siloxane units (10-35 mol.%) where the siloxane units are arranged in nonlinear blocks having at least 2 siloxane units per nonlinear block is new. The organosiloxane block copolymer has a light transmittance of at least 95%.    USE - In a cured product of the organosiloxane block copolymer; in organopolysiloxane block copolymer); preparing electronic article which is further defined as a photovoltaic cell module, as a photovoltaic array that comprises at least two photovoltaic cell modules or as a light emitting diode (all claimed), or solid state light or solid sate lighting such as light emitting diodes (LEDs), which is used in instrument panels, and switches, courtesy lighting, turn and stop signals, household appliances, VCR/DVD/stereo/audio/video devices, toys/games instrumentation, security equipment, switches, architectural lighting, signage (channel letters), machine vision, retail displays, emergency lighting, neon and bulb replacement, flashlights, ascent lighting full color video, monochrome message boards, in traffic, rail, and aviation applications, in mobile phones, PDAs, digital cameras, lap tops, in medical instrumentation, bar code readers, color and money sensors, encoders, optical switches, fiber optic communication; in any industry including, automobiles, small electronics, remote area power systems, satellites, space probes, radiotelephones, water pumps, grid-tied electrical systems, batteries, battery chargers, photoelectrochemical applications, polymer solar cell applications, nanocrystal solar cell applications, and dye-sensitized solar cell applications; in optoelectronic semiconductors, and electronic articles e.g. semiconductors.    ADVANTAGE - The organosiloxane block copolymer has a light transmittance of at least 95%. The combination of the linear diorganosiloxane units (I) and the non-linear siloxane units (II) allow the organosiloxane block copolymer to have a high light transmittance. These linear and non-linear units also tend to allow the organosiloxane block copolymer to flow and cure upon heating yet remain stable at room temperature and also to be able to be processed using lamination techniques. These linear and non-linear units contribute to the physical properties of the organosiloxane block copolymer and allow electronic articles to be formed that are resistant to weather, that can be formed in low cost and low complexity procedures, and that are energy efficient.    DETAILED DESCRIPTION - An organosiloxane block copolymer comprising diorganosiloxane units of formula (R1)2SiO2/2 (I) (65-90 mol.%), where the diorganosiloxane units are arranged in linear blocks having an average of 10-400 diorganosiloxane units per linear block; and siloxane units of formula (R2)x(OR3)ySiO(4-x-y)/2 (II) (10-35 mol.%) where the siloxane units are arranged in nonlinear blocks having at least 2 siloxane units per nonlinear block is new. The organosiloxane block copolymer has a light transmittance of at least 95%.    x=0.5-1.5;    y=0-1;    R1=1-10C hydrocarbyl;    R2=4-10C aryl hydrocarbyl;    R3=R1 or H.    At least 50 mol.% of R2 are aryl. INDEPENDENT CLAIMS are included for the following:    (1) a cured product of the organosiloxane block copolymer;    (2) preparation (M1) of the organosiloxane block copolymer;    (3) an organopolysiloxane block copolymer that is formed by the method (M1);    (4) an electronic article comprising: optoelectronic semiconductor; and encapsulant disposed on the optoelectronic semiconductor and comprising the organosiloxane block copolymer; and    (5) preparation (M2) of the electronic article.