BaSrTiO (BSTO) films have been grown heteroepitaxially on (001) MgO substrates by pulsed laser deposition (PLD) to fabricate microwave phase shifters for the wide frequency range 45 MHz-50 GHz. Both as-grown and ex situ annealed films have a cube on cube epitaxial relationship with 〈100〉BSTO//〈100〉MgO. Threading dislocations are the dominant defects, mostly with Burgers vectors b = 〈101〉. Growth at 10 mbar oxygen pressure, compared to 10 mbar, resulted in significantly better properties. Ex situ annealing of the film grown at 0.1 mbar resulted in a reduction of 40% in threading dislocation density and a 40% increase in dielectric tunability.