No replacement has been named and there has been no announcement about whether Lamouche is moving to a new job.
In Q3 this year, ST has said it will have exited the ST-Ericsson joint venture.
Lamouche's resignation at this stage of the game could be seen as a mark of his dissatisfaction with whatever the proposed plan for the ST - ST-E separation might be.
On the other hand Lamouche will be 54 this year and may well feel he's had enough of what has been a challenging tenure.
Lamouche joined ST as COO in October 2010 in succession to Alain Dutheil.
In November 2011, Lamouche was appointed CEO of ST-Ericsson in succession to Gilles Delfassy.
It was announced when Lamouche was appointed CEO of ST-E that he would be keeping his role as COO of ST.
The first quarterly results for ST-E under Lamouche's tenure as CEO of ST-E were in Q4 2011 when ST-E had a loss of $231m on sales of $409m.
In the last quarterly results of Lamouche's tenure, Q4 2012, ST-E had a loss of $133m on sales of $358m.
Lamouche is a former CEO of Bull.