I live in the UK and am having trouble obtaining semi-sweet chocolate chips in grocery stores. Today I spotted De.Oetker (brand) plain chocolate chips. Would that be the same as semi-sweet, say Nestle' or Hershey's? Package states Cocoa solids 44% minimum.
Yes, dark chocolate of around 35-60% cocoa is essentially semisweet. Higher cocoa percentages are bittersweet.
Not to reduce Elendi's answer, which I am sure is fine, as I am not familiar with UK products:
There is no standardization of the terms like "semi-sweet" or "bittersweet" in the US, either informal or regulatory. The sweetness level is not the only thing that varies with chocolate (or chocolate chips). One of the most important variables is whether or not some or all of the cocoa butter has been replaced with other, less expensive fats, either to change the melting properties, or for economy by the manufacturer. Additionally, there may or may not be emulsifiers or other flavorings.
However, unless you are melting down the chips, they aren't going to participate in the chemistry of the recipe. They are just solid chunks floating in the batter, much like a nut would be. So you can freely use whatever chocolate chip you like--or buy a locally available chocolate bar and chop it up.
Of course, if the question is really regarding what is closest in flavor from your locally available brands, that I could not say.
I've used the Dr. Oetker ones, they aren't as good as US semi-sweet morsels IMHO although they qualify as semi-sweet, and they are ok. If you are willing to splash out a bit more cash Hotel Chocolat ones are much better.
You can usually tell the difference by the amount of added sugar the chocolate chips have -
Bitter or unsweetened dark chocolate has high cocoa solid percentage and little to no sugar added.
Semi-sweet has about 50/50 cocoa solid/butter to sugar ratio.
Bitter-sweet has about 70/30 cocoa solid/butter to sugar ratio.
When in doubt, I say to perform a taste-test.