What semi synthetic, or synthetic blend oils really are, is usualy a Group II conventional base stock with just the necessary amount of usually Group III or a mix of Group III and Group IV PAO, to get it to meet a test or specification that it otherwise would not be able to meet, so the figure in most syn-blends is about 10-15%.
In Europe Semi-Synthetic 10W-40 oils are still extremely popular and sell very well, they usually have specs like SL/CF or SM /CF and A3/B3 or A3/B4.
We also unlike the United States have widespread Passenger car 15W-40 oils, most of these are marketed as being Conventional mineral oils but some are thought to "secretly" also be synthetic blends.