Thermotropic phase behaviors of undiluted A-B type silicone copolymers, Me3SiO-(Me2SiO)(m-2)-Me2SiCH2CH2CH2-O-(CH2CH2O)(n)H (SiC3EOn), have been studied as a function of both poly(dimethylsiloxane) chain length (m) and poly(oxyethylene) chain length (n). Differential scanning calorimetry, small-angle X-ray scattering, and video enhanced microscopy have been employed to construct phase diagrams and characterize microstructures. Three distinct ordered-state morphologies were observed for the Si25C3EOn system: micellar cubic (I-2), hexagonal (H-2) (here, the subscript 2 indicates POE embedded in PDMS matrix), and lamellar (L-alpha), within the examined composition range f = 0.06 to 0.50 (f = volume fraction of the polyoxyethylene part). Only H2 and L. ordered phases were observed in the studied range f = 0.33-0.80 for the SimC3EO51.6 system. The I-2 phase is shown to have Fd (3) over barm or at least Fd (3) over bar space group symmetry. The effective cross-sectional area per copolymer molecule at the A-B interface, alpha(P), increases with increasing both m and n, while the morphologies change in the direction from L-alpha to H-2 with m and I-2 to H-2 to L-alpha with n. The compositional range for the formation of the different microstructures in the absence of solvent is compared with that observed in the presence of solvents (water or silicone oil) and also with other copolymer melt systems.