How to create a new texture by combinig two source textures

I want to create a new texture by drawing texture B (with transparency) over texture A. How to do that?

My idea is to lock the source textures and manually copy pixels from texture B to texture A with taking alpha value for every pixel into account. Is there a better way?

You can also create a render target for the texture you want blended, and rendering to it using drawQuadWithShader with a custom shader that just blends those two textures together. This way GPU does it, which is faster.