We report here the synthesis and dielectric properties of optimized, cross-linked polymer blend (CPB) dielectrics for application in organic field-effect transistors (OFETs). Novel silane cross-linking reagents enable the synthesis of CPB films having excellent quality and tunable thickness (from 10 to similar to 500 nm), fabricated both by spin-coating and gravure-printing. Silane reagents of the formula X3Si-R-SiX3 (R = -C6H12- and X = Cl, OAc, NMe2, OMe, or R = -C2H4-O-C2H4- and X = OAC) exhibit tunable reactivity with hydroxyl-containing substrates. Dielectric films fabricated by blending X3Si-R-SiX3 with poly(4-vinyl)phenol (PVP) require very low-curing temperatures (similar to 110 degrees C) and adhere tenaciously to a variety of FET gate contact materials such as n(+)-Si, ITO, and Al. The CPB dielectrics exhibit excellent insulating properties (leakage current densities of 10(-7) similar to 10(-8) A cm(-2) at 2.0 MV/cm) and tunable capacitance values (from 5 to similar to 350 nF cm(-2)). CPB film quality is correlated with the PVP-cross-linking reagent reactivity. OFETs are fabricated with both p- and n-type organic semiconductors using the CPB dielectrics function at low operating voltages. The morphology and microstructure of representative semiconductor films grown on the CPB dielectrics is also investigated and is correlated with OFET device performance.