The drain current (I
D) transients by switching the biasing condition are examined in FD-SOI MOSFETs with negative biased back gate voltage (V
BG). Special attention is paid to the influence of the gate-induced charge/discharge of the floating body on the I
D transient. The I
D transient appears not only by switching the front gate voltage (V
FG) but also by switching V
BG. It is also shown that the analysis of a small V
FG step transient is useful to examine the lifetime under different bias conditions. All the results can be explained by the
transitional change of I
D − V
FG characteristics at different body-charge conditions.