South Korea's household income gap reached a record high in the fourth quarter of last year.

According to Statistics Korea on Thursday, the average monthly earnings of households in the bottom 20-percent income bracket dropped 17-point-seven percent on-year to one-point-24 million won, the biggest drop since the agency began tracking data in 2003.

The nominal income for the bottom 20-percent plunged 36-point-eight percent from a year earlier to a monthly average of 430-thousand won.

In comparison, the nominal income for households in the upper 20-percent income bracket totaled nine-point-32 million won during the fourth quarter, up ten-point-four percent from the previous year.

These latest trends have led to the country's distribution ratio for disposable income reaching five-point-four-seven, the highest level for any fourth quarter since 2003.

Meanwhile, the average household income for all Korean households increased three-point-six percent to a total of four-point-six million won from October to December.