Should I explain change of major in my statement of purpose? During my masters program I changed my major from Molecular Biology to Biotechnology.
Should I explain in my statement of purpose for PhD programs why I changed my major?
Should I explain in my statement of purpose for PhD programs why I changed my major?


Yes, this is a substantial enough change that it's worth at least a brief explanation.  As a general rule, it's better to explain than to make the committee guess.  There might not be much to say beyond that you realized biotechnology was a better fit for your research interests.  If so, then say that; if there is more to say, then it's worth clarifying further.