Only 10% of over 400,000 IEEE members in more than 160 countries have achieved senior grade.

As per https://www.ieee.org/membership/senior/index1.html, IEEE Senior Member status is evidence of “The professional recognition of" one's "peers for technical and professional excellence.”

IEEE Bylaw I-105.3 sets forth the criteria for elevation to Senior Member Grade, as follows:

“… a candidate shall be an engineer, scientist, educator, technical executive or originator in IEEE-designated fields . The candidate shall have been in professional practice for at least ten years and shall have shown significant performance over a period of at least five of those years." (https://www.ieee.org/membership/senior/senior-requirements.html)